Gear rolling

ABSTRACT

Method and apparatus for forming or finishing gear teeth on a workpiece and particularly for establishing on the workpiece a series of gear teeth formed on a pitch circle essentially concentric with the axis of a central bore in the workpiece. The workpiece is rotated between a pair of forming dies having peripheral gear-forming profiles. Guide surfaces essentially on the pitch circle of the profiles on the dies which cooperates with a guide surface disposed essentially at the intended pitch circle of the gear teeth on the workpiece are brought together under pressure while the profiles on said dies are in rolling engagement with the gear teeth on said workpiece.

United States Patent [72] Inventors Harold R. Sennstrom Waynesboro; John Leonard, Jr., Fayetteville, both of, Pa. [21] Appl. No. 782,605 [22] Filed Dec. 10, 1968 [45] Patented Aug. 17, 19711 [73] Assignee Teledyne Mid-America Corporation Los Angeles, Calif.

[54] GEAR ROLLING 5 Claims, 4 Drawing Figs.

3,469,427 9/1969 Rollins .i 72/91 FOREIGN PATENTS 915,328 7/1954 Germany 72/108 Primary Examiner- Lowell A. Larson Anorney-Strauch, Nolan, Neale, Nies & Kurz ABSTRACT: Method and apparatus for forming or finishing gear teeth on a workpiece and particularly for establishing on the workpiece a series of gear teeth formed on a pitch circle essentially concentric with the axis of a central bore in the workpiece. The workpiece is rotated between a pair of forming dies having peripheral gear-forming profiles, Guide surfaces essentially on the pitch circle of the profiles on the dies which cooperates with a guide surface disposed essentially at the intended pitch circle of the gear teeth on the workpiece are brought together under pressure while the profiles on said dies are in rolling engagement with the gear teeth on said workpiece.

PATENTEDAUBITIH?! 3,599,463

sum 1 BF 3 I NVENTOR 5 HAROLD R. SENNSTROM JOHN LEONARD, JR.

ATTOR EYS PAIENIEBAusmsn' I 3.599.463 sumenra INVENTORS HAROLD R. fizwmsrnom JOHN LEONARD, JR.

ATTOR EYS PATENTEB AUG} mm 3593x1673 sum 3 or 3 INVENTORS HAROLD R. SENNSTROM JOHN LEQNARQJR.

BY J m f TTOEZEYS In accordance with methods and apparatus for forming gears by rolling, which have been known for at least 50 years, gears are roll formed to full depth from cylindrical stock or, alternately, the gear forms may be precut on the workpiece and the rolling process and apparatus usedto impart the final configuration to the workpiece. This'latter method, called gear finishing, is now in widespread use in the production of gears, such as those used in automotive transmissions, which must be manufactured to very close tolerances.

In one such method the gears are finish rolled after being hobbed to rough form, the roll finishing operation being substituted for the prior shaving process. Since most of the metal is removed in the hobbing operation the roll finishing operation requires very little displacement of metal resulting in a significant extension of die life and is thus preferred in many applications. The bobbing operation inevitably creates certain inaccuracies in the gear teeth, particularly when the process is performed on a high production basis. Similarly, it is inherent in the rolling process that inaccuracies in lead, pitch and flank configuration are corrected.

Typical methods and apparatus for finishing prehobbed gear teeth are disclosed in application, Ser. No. 607,455 filed Jan. 5, 1967 and application, Ser. No. 618,750 filed Feb. 27, 1967, each owned by applicants assignee. Briefly, this apparatus comprises a pair of dies having identical peripheral gear-forming profiles, the dies being rotated in the same direction about parallel axes. A previously hobbed workpiece is positioned on a rotatable support between the dies which are then brought together into engagement with the workpiece. The dies and the workpiece then rotate together essentially as a gear train for a short period, i.e., two or three seconds, which is sufficient to finish the gear teeth on the workpiece. The dies are then separated and the workpiece is removed and replaced by a new workpiece. This apparatus has proved to be unexpectedly effective in finishing gears and producing gear teeth of the required dimensional accuracy. Nevertheless, it has been found that when it is applied to the manufacture of larger workpieces it has little effect on the correction of the location of the pitch circle of the gear teeth, which is often eccentric to the axis of the workpiece in the parts produced by the hobbing machine.

Accordingly the use of the above-described gear finishing apparatus has been limited to the production of relatively small gears.

SUMMARY OF THE INVENTION It is the principal purpose and object of the present invention to provide improved gear rolling methods and apparatus for forming gear teeth to final dimensions on a workpiece and particularly to establish or maintain on the workpiece a pitch circle which is essentially concentric with the axis of the workpiece.

lt isa further object of the present invention to provide apparatus for this purpose which is reliable, inexpensive, which has an extended service life, and which can be incorporated on existing machines with minumum modification.

These and other objects of the present invention are attained by locating the dies and the workpiece by positively THE DRAWINGS FIG. l is a top plan view of gear rolling apparatus incorporating the present invention;

FIG. 2 is an enlarged fragmentary vertical section taken along line 22 ofFIG, 1;

FIG. 3 is an enlarged fragmentary horizontal section taken along line 3-3 of FIG. 2; and

FIG. 4 is a view similar to FIG. 3 but showing a modification of the invention.

DESCRIPTION OF PREFERRED EMBODIMENTS For present purposes, the invention will be disclosed herein as applied to apparatus of the type shown in the aforesaid application, Ser. No. 618,750 and in copending application, Ser. No. 763,653 filed Sept. 30, 1968 for Workpiece Feeding Mechanism and owned by applicant's assignee. It is to be understood, however, that the present invention has application to other apparatus of this general type. Briefly, the gear rolling apparatus illustrated in FIG. 1 is of the infeed type in which a workpiece is operated on simultaneously by a pair of opposed identical dies 20 and 22, rotating in the same direction. In the illustrated embodiment of the invention the axis of die 20 is fixed and the axis of the opposed die 22 is laterally shifted between the rolling position shown and a retracted position to permit the removal of the finished workpiece and the positioning of the next piece to be rolled. The die 22 is keyed to a shaft 24 straddle-supported in bearing structures 26 and 28 rigidly secured to the end of a piston associated with the hydraulic power operator indicated generally at 30 carried by the machine bed 32. The opposed die 20 is similarly mounted on a shaft 34 straddle-supported in bearing structures 36 and 38 rigidly mounted on the machine bed 32. The dies 20 and 22 are driven in synchronism in the same direction by a conventional drive mechanism including couplings 40 and 42, telescoping shafts 44 and 46, couplings 48 and 50, connected to the output shaft of gear boxes 52 and 54, driven in conventional manner by a motor 56 through a belt 58.

The internal bore 60 of the workpiece W is supported on the outer end of an arbor assembly 62 rotatably carried by suitable bearings 64 in a turret assembly 66. As more fully explained in the aforesaid copending application, Ser. No. 763,653 the turret assembly 66 is periodically rotated between the position shown and a vertical position. Suitable workpiece handling, feeding and transfer mechanisms indicated generally at 68 and 70, disclosed in detail in the aforesaid copending application are provided to remove finished workpieces from the arbor assembly 62 and replace them with unfinished workpieces in timed operation with the remainder of the apparatus.

When the arbor assembly 62 is moved into the rolling position, shown for example in FIG. 2, the end of a secondary arbor assembly 74 is moved into the end of the primary arbor assembly 62 and the workpiece is securely clamped between shoulders 76 and 78, respectively, on the primary and secondary arbors. The secondary arbor is rotatably supported in a housing 80 mounted for movement axially and laterally of the workpiece as more fully explained in copending application, Ser. No. 618,750. Also, as more fully disclosed in the application the secondary arbor 74 is driven by a prerotator mechanism indicated generally at 82 at least during the initial period of engagement between the dies and the workpiece.

In the operation of the apparatus thus far described, a workpiece having prehobbed gear teeth on its periphery is placed on the arbor assembly 62 which is then brought to the position of FIG. 2 for engagement by the secondary arbor 74. The workpiece is then rotated to produce a surface speed essen tially equal to the surface speed of the die 20 and 22. With the dies and the workpiece rotating in synchronism the die 22 is moved toward the die 20 and simultaneously the axis of the workpiece W is displaced laterally'one-Ihalf the displacement of the axis of the die 22. The dies 20 a 22 then contact opposite portions of the workpiece W simultaneously. In the continued infeed movement of the die 22, the lateral displace ment of the workpiece continues, maintaining the axis of the described is not effective to correct eccentricities of the pitch circle of the workpiece particularly in ears over 3 inches in diameter. In accordance with the present invention this deficiency of the prior machines is eliminated by the provision of a unique system of pilot surfaces which effectively control and positively position the dies and the workpieces during the final stage of the rolling operations.

In a presently preferred form of the invention, as shown particularly in FIG. 3, the pilot or guide surfaces are provided on cylindrical members 84 and 86 carried by the respective shafts 24 and 34 and a cylindrical guide member 88 carried by the arbor assembly 62. The members 84 and 86 are preferably closely fitted onto the shafts 24 and 34 immediately adjacent to the respective dies and 22. The peripheral surfaces 90 and 92 of the guide members 84 and 86 are carefully machined so that they are essentially exactly concentric with the axes of the associated shafts 24 and 34 and are located exactly at the pitch circle of the dies 22 and 20.

To permit its replacement when required, the pilot member 88 is installed on the arbor assembly with a close running fit and again is carefully machined to provide a peripheral guide surface 94 essentially exactly concentric with the axis of the arbor assembly 62 and located at the intended pitch circle of the workpiece W.

With the pilot members 84 and 88 installed the machine is operated as described above. The pilot members do not effect the rolling section until the dies approach full depth position. At this time the pilot surfaces 90 and 92 are in solid rolling engagement with the pilot surface 94 and are maintained in this position by the application of essentially full rolling pressure. Accordingly the dies 20 and 22 are forced to engage the workpiece on a pitch circle which is essentially exactly concentric with the axis of the latter. If the pitch circle of the workpiece is eccentric the eccentricity will be substantially removed by displacing the metal of the individual gear teeth.

The precise nature of the correction is a functionof the eccentricity of the pitch circle on the hobbed part and the extent to which the diameter of the pitch circle on the hobbed part exceeds the pitch circle in the finished part.

Normally, the pitch circle on the hobbed part is substantially oversized, i.e., 0.0010 inches. The hobbed parts are supplied oversize in this amount to assure that sufficient metal will be displaced during the finishing operation to remove all surface imperfections and establish the proper tooth flank configuration.

In the great majority of cases the center of the pitch circle on the hobbed part is offset or eccentric with respect to the center of the bore of the part, by less than 0.005 inches. In such cases, i.e., where the eccentricity is equal to or less than I one-half the difference between the pitch diameter of the hobbed part and pitch diameter of the finished workpiece the rolling operation in accordance with the present invention produces a finished part in which the pitch circle is of the proper diameter and is concentric with the axis of the bore of the part within very close limits, usually within 0.0015 inches.

Inherently, the maximum tooth correction is efiected in the region of the part in which the pitch circle of the hobbed part is offset radially outward from the pitch circle of the finished part and minimum metal displacement and correction will be effected at a point diametrically opposite.

Actual tests have demonstrated that the eccentricity of the pitch line in a hobbed part can be reduced by substantially more than 50 percent with the method and apparatus of the present invention. It is usually effective to reduce the eccentricity to not more than 0.0015 inch which is well within the tolerances required in the manufacture of precision gears.

A modification of the invention to permit. rolling gears with a pitch circle slightly larger or slightly smaller than normal is illustrated in FIG. 4. To this end the pilot member 96 associated with the workpiece is provided with a tapered guide surface 98 and the pilot members 100 and 102 associated with the dies have a slightly crowned pilot surface 104 and 106. The central pilot member 96 is mounted between a pair of nuts 108 and 110 to permit the pilot member 96 to be disposed in any adjusted axial position. It will be apparent that as the pilot member 96 is moved to the left as viewed in FIG. 4 the workpiece W will be rolled with a relatively smaller pitch diameter whereas opposite movement of the pilot member 96 will increased the pitch diameter of the finished part. Apart from the adjustability feature the operation of the embodiment of FIG. 4 is the same as that of FIG. 3.

A particular advantage of both forms of the invention is the protection of the workpiece support structure 62 and 74 from the imposition of high rolling loads. The load distribution is in fact essentially the same as in the apparatus when it is operated without the pilot members, i.e., the rolling loads are absorbed by the shafts 24 and 34 and the associated heavy rigid support structure. Further, bending moments are minimized because of the close juxtaposition of the pilot members with the dies and the workpiece.

The invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.

What I claim and desire to be secured by Letters Patent is:

1. Apparatus for forming gear teeth in a workpiece having a central through bore comprising means supporting said workpiece on said bore for rotation about a predetermined axis, means supporting first and second dies at opposite sides of said workpiece for rotation about axes essentially coplanar with the axis of said workpiece, said dies having peripheral gear-forming profiles, means for relatively moving said workpiece and said dies to bring said dies into forming engagement with said workpiece under pressure, means providing a first guide surface structure associated with said workpiece, and means providing second and third guide surface structures associated respectively with said dies, said second and third guide surface structures being adapted to engage said first guide surface structure when said dies engage said workpiece at the intended pitch circle of said workpiece.

2. The apparatus according to claim 1 wherein said first guide structure comprises a guide member rotatable with said workpiece and having a guide surface corresponding to the intended pitch circle of the gear teeth of said workpiece and said second and third guide surface structures comprise guide members rotatable, respectively, with said dies and having guide surfaces corresponding to the pitch circle of the gear profiles on said dies.

3. Method for altering gear teeth on the periphery of a teeth on said workpiece and the pitch circle of the gear-form ing profiles on said dies, moving said dies into engagement with said workpiece under pressureuntil said second and third surfaces are in rolling engagement with said first surface, and

rotating said dies through at least one revolution while maintaining said surfaces in contact under pressure. 4. Method for forming gear teeth on a workpiece having a central through bore, supporting said workpiece bore and rotating said workpiece about an axis parallel and adjacent to the axis of a rotatable die having a peripheral gear-forming profile, providing first and second cylindrical stop surfaces, respectively, essentially at the pitch circle of the gear teeth on the workpiece and at the pitch circle of the gear profile on said die, moving said die into engagement with said workpiece under pressure until said first and second surfaces are in rolling engagement, then rotating said die through at least one revolution while maintaining said surfaces in contact under pressure while simultaneously restraining said workpiece against movement laterally of its axis.

5. Method for altering gear teeth on the periphery of a workpiece having a through bore to render the pitch circle of said gear teeth essentially concentric with the axis of said bore comprising the steps of supporting said workpiece bore and rotating said workpiece adjacent a rotatable die having a UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 599 Dated August 17, 1971 Harold R. Sennstrom et al. Inventor(s) It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

The figure of drawing appearing on the first page of the Patent should he canceled and the figure shown on the attached sheet substituted therefor..

Abstract, line 53, eooperates" should be -cooperate-.

Col. 2, line 68, 'die" should be -dies-.

Col. 2 line 72, "a" should be and.

Col. 3, line 11, "ears" should be -gears.

Col. 4, line 16, "increased" should be -increase--.

Signed and sealed this 6th day of March 1973.

(SEAL) Attest:

EDWARD N FLETCHER ,JR ROBERT GUTTSCHALK Attesting Officer Commissioner of Patents USCOMM-DC 50376-P69 ORM PC4050 {10-691 0 us GOVERNMENT PRINTING orncz lass c ases. 

1. Apparatus for forming gear teeth in a workpiece having a Central through bore comprising means supporting said workpiece on said bore for rotation about a predetermined axis, means supporting first and second dies at opposite sides of said workpiece for rotation about axes essentially coplanar with the axis of said workpiece, said dies having peripheral gear-forming profiles, means for relatively moving said workpiece and said dies to bring said dies into forming engagement with said workpiece under pressure, means providing a first guide surface structure associated with said workpiece, and means providing second and third guide surface structures associated respectively with said dies, said second and third guide surface structures being adapted to engage said first guide surface structure when said dies engage said workpiece at the intended pitch circle of said workpiece.
 2. The apparatus according to claim 1 wherein said first guide structure comprises a guide member rotatable with said workpiece and having a guide surface corresponding to the intended pitch circle of the gear teeth of said workpiece and said second and third guide surface structures comprise guide members rotatable, respectively, with said dies and having guide surfaces corresponding to the pitch circle of the gear profiles on said dies.
 3. Method for altering gear teeth on the periphery of a workpiece having a through bore to render the pitch circle of said gear teeth essentially concentric with the axis of said bore comprising the steps of supporting the bore of said workpiece and rotating said workpiece between a pair of opposed rotatable dies, providing first, second, and third stop surfaces positioned, respectively, essentially at the pitch circle of the gear teeth on said workpiece and the pitch circle of the gear-forming profiles on said dies, moving said dies into engagement with said workpiece under pressure until said second and third surfaces are in rolling engagement with said first surface, and rotating said dies through at least one revolution while maintaining said surfaces in contact under pressure.
 4. Method for forming gear teeth on a workpiece having a central through bore, supporting said workpiece bore and rotating said workpiece about an axis parallel and adjacent to the axis of a rotatable die having a peripheral gear-forming profile, providing first and second cylindrical stop surfaces, respectively, essentially at the pitch circle of the gear teeth on the workpiece and at the pitch circle of the gear profile on said die, moving said die into engagement with said workpiece under pressure until said first and second surfaces are in rolling engagement, then rotating said die through at least one revolution while maintaining said surfaces in contact under pressure while simultaneously restraining said workpiece against movement laterally of its axis.
 5. Method for altering gear teeth on the periphery of a workpiece having a through bore to render the pitch circle of said gear teeth essentially concentric with the axis of said bore comprising the steps of supporting said workpiece bore and rotating said workpiece adjacent a rotatable die having a peripheral gear forming profile, providing first and second stop surfaces positioned, respectively, essentially at the pitch circle of the gear teeth on said workpiece, and the pitch circle of the gear-forming profile on said die, moving said die into engagement with said workpiece under pressure until said first and second surfaces are in rolling engagement, and rotating said die through at least one revolution while maintaining said first and second surfaces in contact under pressure while simultaneously restraining said workpiece against movement laterally of its axis. 